The present invention relates to a fine forging method that can be used for manufacture of such components as a liquid ejection head, a manufacturing method of a liquid ejection head, and a liquid ejection head.
Liquid ejection heads for discharging ejects of pressurized liquid from nozzle orifices are known that deal with various liquids. Such liquid ejection heads are mainly used as recording heads for image recording apparatus such as printers and plotters. In recent years, by making use of their feature that they can correctly supply very small amounts of liquid to prescribed locations, they have come to be applied to various manufacturing apparatus as, for example, colorant ejection heads for manufacturing apparatus for manufacture of color filters of liquid crystal displays etc., electrode material ejection heads in manufacturing apparatus for formation of electrodes of organic EL (electroluminescence) displays, FEDs (field emission displays) etc., bioorganic material ejection heads in manufacturing apparatus for manufacture of biochips. Recording heads eject liquid ink and colorant ejection heads eject colorant solutions of E (red), G (green), and B (blue). Electrode material ejection heads eject a liquid electrode material and bioorganic ejection heads eject a solution of a bioorganic material.
Ink jet recording heads are typical examples, and an ink jet recording head will be described below as a conventional technique.
Among various kinds of ink jet recording heads (hereinafter referred to as recording heads), what is called an on-demand recording head which is now widely spread have a plurality of channels that correspond to respective nozzle orifices and extend from a common ink chamber to the nozzle orifices via pressure generation chambers. To satisfy the requirement of downsizing, the pressure generation chambers need to be formed at a fine pitch that corresponds to a recording density. Therefore, partitions of the adjoining pressure generation chambers are very thin. To efficiently convert ink pressure fluctuation in the pressure generation chamber to ejection force of ink droplets, the width of ink supply holes through which the pressure generation chambers communicate with the common ink chamber is smaller than the width of the pressure generation chambers. To form those minute pressure generation chambers and ink supply holes with high dimensional accuracy, the conventional recording head employs a silicon substrate preferably. More specifically, a crystal face is exposed by silicon anisotropic etching and pressure generation chambers and ink supply holes are formed on the crystal face.
To meet the requirements of high workability etc., a nozzle plate that is formed with nozzle orifices is made of a metal plate. Diaphragm portions for changing the volumes of pressure generation chambers are formed on an elastic plate. The elastic plate has a double-layer structure that a resin film is bonded to a metal support plate and portions of the support plate facing the respective pressure generation chambers are removed.
Incidentally, in the above-described conventional recording head, because the partitions are very thin, it is difficult to correctly obtain the recess shape of the pressure generation chambers and to set the liquid accommodation volume of the pressure generation chambers etc. In particular, the recess shape is long and narrow. To finish the partitions sharply, it is important to precisely determine the shapes of the end portions, in the longitudinal direction, of the recess shape.
Further, because of a large difference between the linear expansion coefficients of silicon and the metals, it is necessary that the silicon substrate, the nozzle plate, and the elastic plate be bonded to each other at a relatively low temperature by spending a long time. This makes it difficult to increase the productivity and is a cause of increase of the manufacturing cost.
In view of the above, to increase the productivity and for other purposes, in the above type of liquid ejection head, attempts have been made to form liquid channels in a metal pressure generation plate (e.g., patent documents 1 and 2). That is, these patent documents disclose methods for forming, by plastic working (e.g., face pushing or press working) on a metal plate, supply holes through which a reservoir and pressure chambers communicate with each other, recessed grooves to serve as the pressure chambers, and communication holes through which the pressure chambers and nozzle orifices communicate with each other.
However, since, for example, the pressure generation chambers are very fine and the channel width of needs to be smaller than the width of the pressure generation chambers, problems arise that the working is difficult and it is difficult to increase the production efficiency.
On the other hand, this type of liquid ejection head is required to discharge very small amounts of liquid ejects. This is because, in the case of ink jet recording heads, the use of very small amounts of ink ejects can increase the number of dots to reach a unit area and hence makes it possible to record high-quality images with low graininess. In the case of colorant ejection heads, decreasing the amounts of ejects can reduce the area of each pixel and hence makes it possible to manufacture high-resolution displays (or filters). In the case of electrode material ejection heads, decreasing the amounts of an electrode material makes it possible to form very narrow conductors in a desired pattern.
The above-mentioned patent documents 1 and 2 are Japanese Patent Publication No. 55-14283A (page 2 and FIG. 6) and Japanese Patent Publication No. 2000-263799A (pages 6-9 and FIGS. 4-14), respectively.
However, it has been found that several problems arise when it is attempted to produce, by the methods of the above patent documents, a liquid ejection head capable of satisfying current requirements. One of those problems relates to bubble ejection performance.
To produce a liquid ejection head capable of discharging very small amounts of liquid ejects, the width of the groove-shaped recesses to serve as the pressure chambers necessarily becomes very small. Further, the groove-shaped recesses need to be arranged close to each other in the groove width direction. However, it is difficult for the methods of the above patent documents to form all the communication holes at one ends, in the longitudinal direction, of the groove-shaped recesses. For example, as shown in FIG. 25A, there is no other way than forming each communication hole 34 at a position that is separated, in the groove longitudinal direction, from a longitudinal end face (recess end face) 70 of a groove-shaped recess 33. This is because of a positional variation of the recess end faces 70.
In this case, forming the groove-shaped recesses 33 by press working causes a variation of the positions of the recess end faces 70 among the groove-shaped recesses 33. Therefore, if it is attempted to form the communication holes 34 right adjacent to the groove-shaped recesses in the longitudinal direction as shown in FIG. 25B, part of punches may act on the thick portion of a metal plate. Since the punches are very thin, punches acting on the thick portion may bend or buckle. Therefore, in forming the communication holes 34, it is necessary that all the punches be positioned with proper margins so as to go into the groove-shaped recesses 33 completely. As a result, the punches are separated from the respective recess end faces 70 and hence the communication holes 34 are also formed so as to be separated from the respective recess end faces 70.
If in this manner the communication holes 34 are formed so as to be separated from the respective recess end faces 70, flat portions 71 are formed between the recess end faces 70 and the communication holes 34. The flat portions 71 are a cause of stay of bubbles, that is, a factor of hindering removal of bubbles. That is, the presence of the flat portions 71 causes stagnation in the liquid flowing through each pressure chamber, and bubbles in the liquid stay in the stagnant portion and are hard to remove. Further, if such bubbles grow large, they may influence the liquid jet discharge characteristics (e.g., the flying speed and the amount of discharge) or hinder a liquid flow.
As described above, forming pressure generation chambers by plastic working on a metal substrate has the problem that turbulence occurs in ink or bubbles pile up depending on the shapes of the inner surfaces of each pressure generation chamber formed and the shapes of the portions close to each of the communication holes through which the pressure generation chambers communicate with the nozzle orifices, which may adversely affect the liquid ejection characteristics.
The present invention has been made in view of the above circumstances, and a first object of the invention is to allow ink to flow smoothly in the pressure generation chambers and prevent the stay of bubbles by precisely forming the partitions including both end portions thereof by performing highly accurate working to form recess shapes for the pressure generation chambers etc. That is, the first object of the invention is to improve the bubble ejection performance by improving the shapes of the end portions of the groove-shaped recesses.
A second object of the invention is to precisely form the partitions including both end portions thereof by performing highly accurate working to form recess shapes for the pressure generation chambers etc.